Mention of CB caps triggers story mode (yeah, I'm old and proud of it... I should be dead).
TL;DR: CB caps be way more powerful than a Sheridan 5mm pump-up air rifle, which was top-heap powerful in 1966.
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Circa 1966, I bought a box of CB caps someplace... back then, 14-year-olds out hunting or driving powerboats didn't raise an eyebrow, so buying .22 ammo wasn't really noteworthy. Anyway, I had a Sheridan 5mm pellet rifle that I shot every day, often at backstop made of a cardboard box stuffed with a few magazines and newspapers (folded, not wadded --> more dense). The backstop was on the floor of my dad's metal shed in the back yard - kept backstop out of the rain; I just opened the door to shoot.
That Sheridan rifle would put a pellet through a 1/4" sheet of plywood, and my backstop reliably stopped them with layers of magazine/newspaper to spare. So I figured it would be adequate for CB caps.
So I loaded a CB cap into my single-shot .22, aimed, and let fly. WHACK RATTLE Rattle silence.
The bullet went through my backstop and rattle-bounced off the walls of the shed - fortunately didn't go THROUGH the wall.
Dad would have, um, been irate had he or my mother known about my little experiment. Lesson learned, mouth shut.